1. Field of the Invention
The present invention relates to a mounting structure for a two-terminal capacitor and three-terminal capacitor.
2. Description of the Related Art
Up to now, in order to reduce the equivalent series inductance of a two-terminal capacitor for eliminating noise current used in power supply lines of high-speed ICs, for example, as shown in FIG. 15, a plurality of two-terminal capacitors 1A and 1B are mounted on a circuit board 30 such that the two-terminal capacitors 1A and 1B are electrically connected in parallel between a hot conductor pattern 60 and a grounding conductor pattern G11. That is, when the equivalent series inductance is required to be one half, two two-terminal capacitors are mounted in parallel and, when it is required to be one third, three two-terminal capacitors are mounted in parallel. Moreover, in FIG. 15, arrows Ia and Ib represent the direction in which the noise currents flow in the capacitors 1A and 1B.
Accordingly, in order to realize a lower equivalent series inductance, many capacitors are required to be mounted on the circuit board 30 and a large mounting space is necessary, which is one factor of high cost.
In order to overcome the problems described above, preferred embodiments of the present invention provide a mounting structure for a two-terminal capacitor and three-terminal capacitor, in which the equivalent series inductance of the capacitors is greatly reduced and the mounting space required is small and which is very low cost.
In a two-terminal capacitor mounting structure according to a preferred embodiment of the present invention, at least two two-terminal capacitors, each having a chip element and a first external terminal and a second external terminal provided on both ends of the chip element respectively, are mounted on a circuit board having a first conductor pattern and at least two second conductor patterns arranged so as to interpose the first conductor pattern therebetween. In the two-terminal capacitor mounting structure, the two two-terminal capacitors are arranged so that noise currents flowing in the two two-terminal capacitors may be in opposite direction to each other with respect to the first conductor pattern or the sum of directional vectors of the noise currents may be zero such that the first external terminal of each of the at least two two-terminal capacitors is electrically connected to the first conductor pattern, such that the second external terminal of one of the two two-terminal capacitors is electrically connected to one of the two second conductor patterns, and such that the second external terminal of the other two-terminal capacitor is electrically connected to the rest of the two second conductor patterns.
According to the above-described unique construction, the noise currents (high-frequency currents) flowing in the two two-terminal capacitors become opposite in direction relative to each other. Therefore, the magnetic fields generated by these noise currents cancel each other out. As a result, the equivalent series inductance generated by the two two-terminal capacitors is greatly reduced and minimized to substantially less than one third.
Furthermore, in a two-terminal capacitor mounting structure according to a preferred embodiment of the present invention, a grounding conductor pattern is arranged so that noise currents flowing in the grounding conductor pattern and noise currents flowing in the two-terminal capacitors may be in opposite direction to each other or the sum of directional vectors of the noise currents may be zero in such a manner that the grounding conductor pattern is provided at least either inside the circuit board or on the rear surface of the circuit board and such that the grounding conductor pattern is electrically connected to one of the first conductor pattern and second conductor patterns and to grounding external terminals of the two-terminal capacitors through an electrical connector provided inside the circuit board.
According to the above-described unique construction, noise current flowing in an opposite direction relative to the noise current flowing in the two-terminal capacitors flows in the grounding conductor pattern provided inside the circuit board or on the rear surface of the circuit board. Therefore, the magnetic fields generated by these noise currents cancel each other out. As a result, the total equivalent series inductance of the two-terminal capacitors and the circuit board is greatly reduced.
Furthermore, in a three-terminal capacitor mounting structure according to a preferred embodiment of the present invention, a three-terminal capacitor, which has a chip element, through electrodes provided inside the chip element, internal electrodes arranged so as to face the through electrodes, a first external terminal and a second external terminal provided on both ends of the chip element respectively and electrically connected to the through electrodes, and third external terminals provided on side surfaces of the chip element and electrically connected to the internal electrodes, is mounted on a circuit board having hot conductor patterns and a grounding conductor pattern. In the three-terminal capacitor mounting structure, the three-terminal capacitor is mounted on the circuit board and the grounding conductor pattern is arranged so that noise currents flowing in the grounding conductor pattern and noise currents flowing in the three-terminal capacitor may be in opposite direction to each other such that the first external terminal and the second external terminal are electrically connected to the hot conductor patterns in the three-terminal capacitor, such that the grounding conductor pattern is provided either inside the circuit board or on the rear surface of the circuit board, and such that the grounding conductor pattern is electrically connected to the third terminals of the three-terminal capacitor through an electrical connector provided inside the circuit board.
Alternatively, in a three-terminal capacitor mounting structure, the three-terminal capacitor is mounted on the circuit board and the hot conductor patterns are arranged so that noise current in the hot conductor pattern and noise currents flowing in the three-terminal capacitor may be in opposite direction to each other such that the third external terminals are electrically connected to the grounding conductor pattern in the three-terminal capacitor, such that the hot conductor patterns are provided either inside the circuit board or on the rear surface of the circuit board, and such that the hot conductor patterns are electrically connected to the first external terminal and the second external terminal through an electrical connector disposed inside of the circuit board.
According to the above-described unique construction, noise current flowing in an opposite direction relative to the noise current flowing in the three-terminal capacitor flows in the grounding conductor pattern and the hot conductor patterns provided inside the circuit board or on the rear surface of the circuit board. Therefore, the magnetic fields generated by these noise currents cancel each other out. As a result, the total equivalent series inductance of the three-terminal capacitor and the circuit board is greatly reduced.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.